Leak detection system for a nuclear reactor

ABSTRACT

An elongated slide valve for detecting fuel leaks in a nuclear reactor has a plurality of sampling ports along one side of a valve body and a plurality of intermittently spaced flush ports along an opposing side of the valve body. A slide member alternately communicates with sampling port and flushing port as it sequentially samples the various fuel subassemblies of the reactor through the sampling ports. A single outlet chamber and throughgoing conduit exits each sample from the nuclear reactor to monitoring equipment. The reactor coolant is employed as the flush between samples and as the seal for the slide member. The slide valve is operated by the control rod drive mechanism.

United States Patent 1 [111 3,801,440

Apt, Jr. et a]. Apr. 2, 1974 [54] LEAK DETECTION SYSTEM FOR A 308,8513/1967 Zoludow l37/625.48 X

NUCLEAR REACTOR Primary Examiner-Reuben Epstein [75] Inventors figzg s ggg Jr an Attorney, Agent, or FirmWebb, Burden, Robinson &

9 9 S of Pittsburgh, Pa. Webb [73] Assignee: USC Incorporated,Pittsburgh, Pa. [57] ABSTRACT 2 Filed; No 3 9 1 An elongated slide valvefor detecting fuel leaks in a nuclear reactor has a plurality ofsampling ports along [21] Appl' N05 195,419 one side of a valve body anda plurality of intermittently spaced flush ports along an opposing sideof the 52 us. Cl. 176/1 9 LD, 137/625.48 valve body- A Slide memberalternately communicates 51 rm. cu G21c 17/04 with Sampling P andflushing P as it sequentially [58] Field of Search 176/19 R, 19 LD;samples the Various fuel Subassemblies of the reactor 137/625.48, 625.68through the sampling portsv A single outlet chamber and throughgoingconduit exits each sample from the 5 R f r Cited nuclear reactor tomonitoring equipment. The reactor UNITED STATES PATENTS coolant isemployed as the flush between samples and as the seal for the slidemember. The slide valve is opgzz' i i 137/625; X erated by the controlrod drive mechanism. 3,293,934 12/1966 Schaeffer et al l37/625.48 X 1Claim, 10 Drawing Figures nnnnnvn"u".....,..,......d.)//l' PATENTEHAPR21914 $801,440

l 25 INVENTORS. Jerome Apf, Jr.

William J. Wachrer Wesley M. Rohreudr.

Br b/ 0 1: 19.7 M

THE/R ATTORNEYS LEAK DETECTION SYSTEM FOR A NUCLEAR REACTOR Ourinvention relates to fluid cooled nuclear reactors and, moreparticularly, to a detecting system for reveal ing defects in the fuelsubassemblies of the nuclear reactor.

A number of detecting systems are known for reveal ing ruptures orsimilar faults in the cladding which surrounds the individual fuel pinsin the reactor core fuel subassemblies. In the event of a fault in thecladding, the radioactivity which escapes from the fuel pin contaminatesthe fluid coolant flowing along the fuel subassemblies. The increase inradioactivity of the coolant is detected by a main monitoring systemwhich measures the radioactivity of the coolant as it flows out of thereactor.

Since a nuclear reactor contains a large number of fuel subassemblies,each of which is comprised ofa plurality of individual fuel pins, it isnecessary to not only know when there is a substantial leak in aparticular fuel subassembly, but it is also necessary to locate andverify which particular fuel subassembly is defective. Conventionaldetecting systems include a large number of separate sampling conduits,usually one for each fuel subassembly, which pass through the reactor toan exterior monitoring system. This, of course, necessitates the needfor a large number of throughgoing conduits with valves and sealingmaterial, etc.

Several internal valving systems have been suggested in which rotaryvalves are employed within the reactor with only a few conduits passingthrough the reactor wall to the monitoring system. However, these rotaryvalves, for the most part, have proven unreliable because of thecomplexities required to handle so many incoming samples without sampleto sample dilution or mixing.

Our invention overcomes the disadvantages of the known detecting systemsand provides a system which can function successfully while the reactoris operating, regardless of the power level. In addition, the system isas sensitive as the sensitivity of the monitoring device and thepresence of high radiation backgrounds and primary loop contaminatesdoes not affect the functioning or sensitivity of the system. Further,the system inherently is capable of discriminating between normalprimary coolant contamination and the results of fuel pin claddingfailures.

The system operates effectively regardless of the fuel, the geometry ofthe fuel pins or the type of coolant employed. In addition, the systemis very compact and operable from existing equipment, thus requiring noadditional design to the normal reactor. The system can both detect theexistence of a failed fuel pin and also verify its location and thesignals from the system can be remotely indicated or stored and arecompatible with standard analog digital date handling equipment.

The environment present at the particular nuclear reactor site has noeffect on the system and, because the system is wholly integrated, thereis no need for systems other than the normal existing monitoring andanalysis system which provides normal cover gas analysis and reactorcoolant discharge analysis.

Our invention is a multi-port elongated slide valve in which thesampling ports are positioned along one side of the valve body and aplurality of flush ports are positioned on the opposing side of thevalve body with a flushing port being positioned intermediate adjacentsampling ports. A movable slide member operates within the valve body toalternately smaple from a sampling port and a flush port whilesequentially sampling each sampling port which communicates with thevarious fuel subassemblies. The reactor coolant acts both as the flushbetween successive samples and as a seal for the slide member. A singleoutlet chamber having an outlet orifice communicates with a centralsample duct of the slide member and with a leak detection monitoringsystem on the exterior of the reactor. The slide valve is operated bythe control rod drive mechanism.

In the accompanying drawings, we have shown a presently preferredembodiment of our invention in which:

FIG. 1 is a section through our slide valve;

FIG. 2 is an enlarged broken away section of the slide valve;

FIG. 3 is a section taken along lines III-Ill of FIG.

FIG. 4 is a section taken along lines lV--IV of FIG.

FIG. 5 is a section taken along lines V-V of FIG. 2;

FIG. 6 is a section taken along lines VIVI of FIG.

FIG. 7 is a section taken along lines VIIVII of FIG.

FIG. 8 is a representation of the flushing ports and the sampling portsand the tubing directed thereto from the fuel subassemblies;

FIG. 9 is a section of a modified slide head; and

FIG. 10 is a section through another modified slide head.

A nuclear reactor contains many fuel subassemblies, each of which ismade up of a large number of individual fuel pins. These fuelsubassemblies are normally divided into groups with each group beingoperable through a particular control in a given sector of the nuclearreactor. Each sector of the nuclear reactor normally has an instrumenttree column which supports and contains the instrumentation, controlrods and scram rods for the fuel subassemblies and ancillary equipmentwithin that particular sector. Our detection system is adaptable formounting to such an instrument tree and in a typical nuclear reactorhaving three sectors, there will be three detection systems employed.Our device is compatible with any of the existing nuclear reactors whichare fluid cooled and with any of the existing fluid coolants be theywater, gas or liquid metals.

Our detection system comprises a slide valve 10 having an elongatedvalve body 11 and an elongated slide member 12 operable therein, FIGS. 1and 2.

The valve body 11 is cylindrical and contains along the bottom portionthereof a plurality of equally spaced and aligned sampling ports 13along one side of the valve body 11. Specifically, twenty seven samplingports 13 are shown and will sample twenty seven separate fuelsubassemblies (not shown) in the nuclear reactor. A plurality of spacedand aligned flush ports 14 are positioned removed about the cylindricalvalve body 11 from the sampling ports 13. It is necessary that a flushport 14 be positioned between each two sampling ports 13 which areadjacent each other.

In addition, a flush port 14 will also be positioned at the extreme topand/or bottom of the aligned ports so that each sampling cycle starts orends with a sample from a flush port 14. The flush ports 14 arepositioned at one-half pitch or midway between the sampling ports 13 forreasons to be described hereinafter. The flush ports 14 are open to thereactor plenum and the standard reactor coolant passes therethrough.

The elongated slide member 12 is freely positioned within thecylindrical valve body 11 and is mounted at its upper end on a longshaft 15, FIGS. 1-3, driven by a standard control rod drive mechanism,not shown. The control rod drive mechanism is primarily used to operatethe control and scram rods, but is easily adapted to control thesequential sampling operation of g the detection system.

The control drive mechanism is normally an electromechanical device,although hydraulic and pneumatic systems have also beem employed. Thecontrol drive itself imparts a linear or swinging motion to the controlrods. This is normally accomplished through a slowspeed, reversibledrive in which there is a high-speed overriding drive to operate thescram rods in case of the need for a rapid reactor shutdown. Our novelmethod of operation is the use of the control drive mechanism to operatethe leak detection apparatus. The exact mechanical hook-up and thecomponents for the sequential control of the sampling do not form a partof this invention. It will be recognized by those skilled in the artthat a variety of known hook-ups and components to control a sequentialsampling can be employed.

Slide member 12 has an upper section which defines an outlet chamber 16,generally annular, between the outer slide wall and the inner wall ofthe valve body 11, FIG. 4. Outlet chamber 16 in turn communicates withmonitoring equipment external of the reactor via throughgoing conduit 26which connects to chamber 16 at orifice 27. The lower section of theslide member defines an annular chamber 17 of substantial cross section,FIGS. and 6, between the outer slide wall and the inner wall of thevalve body 11. This annular chamber 17 communicates with and is open tothe flush ports 14 and the sampling ports 13.

The slide member 12 terminates in an enlarged piston type head 18, FIGS.2 and 7. A central duct 19 extends longitudinally through the slidemember 12 and terminates at its upper end in a crossover duct 20 whichcommumicates with outlet chamber 16. The central duct 19 communicates atits lower end with a sampling duct 21 in the enlarged head 18. Thesampling duct 21 extends from the central duct 19 transversely throughthe head 18 in the direction of the sampling ports 13 and terminates inan annular chamber 22 which encircles and is recessed within the head18. The central duct 19 actually extends through head 18 and is shut offby plug 23 which threadably engages head 18. This plug arrangement isemployed to simplify the manufacture of the elongated slide member 12.

The head 18 is critically dimensioned to form a slight gap 24 betweenthe head 18 and the inner wall valve body 11, and thus allow freemovement and prevent binding between head 18 and the inner wall of valvebody 11, FIGS. 6 and 7. Head 18 is also dimensioned so that when thesampling duct 21 is directly aligned with a sampling port 13, the head18 will extend between adjacent flushing ports 14, FIG. 2.

Each sampling port 13 is connected to a particular fuel subassemblyoutlet or group of subassembly outlets by means of tubing 25. Thistubing 25 will normally extend from the sampling port 13 to the axialcenter line of a particular fuel subassembly, not shown. Because of thelarge number of sampling tubes 25 necessary, the

tubes 25 from adjacent sampling ports 13 are staggered to maximize thecompactness of the large array of tubes 25, FIG. 8. This staggeredrelationship permits the tubes 25 to be completely supported from theinstrument column so as to prevent flowdriven vibrations.

The actual sampling of the fuel subassemblies is accomplished throughthe inherent pressure differentials within the reactor itself whichprovides for the movement of coolant from an..area of high pressure toan area of low pressure. When the slide member 12 is positioned by thecontrol drive mechanism so that the sampling duct 21 is in directalignment with a sampling port 13, the coolant from the sampling portand the particular fuel subassembly communicating therewith will bedrawn into the central duct 19 because of the lower pressure within thecentral duct 19. Because of the constriction of gap 24, the pressurefrom the sampling port 13 will be greater than from the flush ports 14and, therefore, the sample will not be diluted by the coolant. However,the coolant from the flush ports 14 provides a seal between the enlargedhead 18 and the valve body 11.

When the slide member 12 is moved by the control drive mechanism so thatthe annular chamber 22 of head 18 is in alignment with a flush port 14,the pressure will be greater at the flush port than from the fluidleakage at the sample ports 13 and, therefore, the reactor coolant willbe drawn into the central duct, as a flush.

In other words, reactor coolant is continually entering and leavingchamber 17 through the flush ports 14 and coolant from sampling ports 13is also continually bled into chamber 17, but these coolants do notdilute or mix with the particular sample or flush being taken.

The fluid sample in the central duct 19 passes into the outlet chamber16 via the crossover duct 20 and through the orifice 27 and conduit 26into the monitoring equipment on the exterior of the reactor. By knowingthe dwell time, that is, the time it takes a sample to travel a knowndistance under known conditions, the monitoring equipment candistinguish between the particular sample from a sampling port and theflush coolant.

The slide member 12 moves in sequence from a sampling port 13 to a flushport 14 and then to the next sampling port 13 in a timed sequence, thissequence being programmed into the control drive mechanism. The sequencemay be monitored so that when a leak is detected from a sampling port13, an additional time period for sampling is automatically programmedto verify the leakage at that sampling port 13. Of course, the readoutfrom the monitoring equipment will identify the particular fuelsubassembly from which the sample is being taken.

It is also possible to monitor the reactor coolant from the flush ports14 to identify the particular sector of the reactor having coolantcontamination. Presently only the coolant at the discharge end of threactor is monitored, in which case one only knows that there is a leaksomewhere in the reactor. In other words, the flush coolant can bemonitored to detect the particular sector of the reactor which has afailed fuel subassembly or subassemblies and then the particular fuelsubassembly which has caused the failure is also identified and thenverified by the additional sample time at that particular fuelsubassembly.

The slide valve can be modified in several respects and still accomplishthe same result. For example, the slide member 12 need not include theannular chamber 22. In this situation the sampling duct extends clearthrough the enlarged head 18 to permit the withdrawing of a sample or aflush, as the case may be, into the central duct 19, FIG. 9. Thesampling duct 21' need only extend as in the preferred embodiment, FIG.10. In this latter instance the slide member 12' is rotated 180 as itmoves from sample port to flush port, thereby again accomplishing thedesired sequential sampling. A plurality of chambers can be recessedradially outward from the valve body in the area of the sampling portsand/or flush ports, but this arrangement is somewhat impractical and isnot illustrated.

We claim:

1. In a leak detection system for a nuclear reactor of the fluid cooledtype and having an external leakage detection monitoring means, theimprovement comprising a slide valve adapted to be supported internal ofthe reactor and having an elongated cylinder member with a plurality ofequally spaced sampling ports 6 aligned along a lower portion of thecylinder and a plurality of equally spaced flush ports aligned removedfroin the sampling ports, a flushing port being positioned between eachadjacent sampling ports, said sampling ports adapted to connect tovarious reactor fuel subassemblies through sampling tubes and saidflushing ports open to the reactor coolant, a movable slide member fullypositioned within the cylinder, said slide member cooperating with thecylinder to define an outlet chamber along the upper portion of thecylinder, said outlet chamber adapted to connect to the monitoring meansvia a throughgoing conduit and an annular chamber extending along theslide member and terminated by an enlarged sampling head, said headhaving a sampling duct therein for direct alignment with the samplingports and communicating with the outlet chamber through a central ductin the slide member, said sampling head also including an annularperipheral chamber communicating with the sampling duct, said samplinghead dimensioned to form a slight gap between the head and cylinder andto extend between adjacent flush ports when the sampling duct is indirect communication with a sampling port, whereby said sampling memberalternately aligns with a sampling port and a flush port to sequentiallydraw samples from all the sample ports, said coolant from the reactoracting both as the flush and the seal for the slide valve. =l=

1. In a leak detection system for a nuclear reactor of the fluid cooledtype and having an external leakage detection monitoring means, theimprovement comprising a slide valve adapted to be supported internal ofthe reactor and having an elongated cylinder member with a plurality ofequally spaced sampling ports aligned along a lower portion of thecylinder and a plurality of equally spaced flush ports aligned 180*removed from the sampling ports, a flushing port being positionedbetween each adjacent sampling ports, said sampling ports adapted toconnect to various reactor fuel subassemblies through sampling tubes andsaid flushing ports open to the reactor coolant, a movable slide memberfully positioned within the cylinder, said slide member cooperating withthe cylinder to define an outlet chamber along the upper portion of thecylinder, said outlet chamber adapted to connect to the monitoring meansvia a throughgoing conduit and an annular chamber extending along theslide member and terminated by an enlarged sampling head, said headhaving a sampling duct therein for direct alignment with the samplingports and communicating with the outlet chamber through a central ductin the slide member, said sampling head also including an annularperipheral chamber communicating with the sampling duct, said samplinghead dimensioned to form a slight gap between the head and cylinder andto extend between adjacent flush ports when the sampling duct is indirect communication with a sampling port, whereby said sampling memberalternately aligns with a sampling port and a flush port to sequentiallydraw samples from all the sample ports, said coolant from the reactoracting both as the flush and the seal for the slide valve.